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List:       freetype
Subject:    Re: [ft] Using different loading and render modes, plus LCD example
From:       Aekold Helbrass <helbrass () gmail ! com>
Date:       2011-06-16 15:34:32
Message-ID: BANLkTi=UV3fwPMZeLmtXbX1k=wpakdsOQQ () mail ! gmail ! com
[Download RAW message or body]

Thank you, finally figured out how to use LCD bitmap with QImage.
Small piece of source code below. But still have a problem: there is a
lot of noise on rendering, and that noise is jumping on repainting of
component. So it looks like I've done something wrong with color
transformations. Basically I am filtering out white pixels, but there
are a lot of "almost white" ones. Please see attachment.

source code (cut out error handling to show only logic part):

            error = FT_Load_Glyph( m_face, glyph_index, FT_LOAD_TARGET_LCD);
            error = FT_Library_SetLcdFilter(m_library, FT_LCD_FILTER_DEFAULT);
            error = FT_Render_Glyph( m_face->glyph, FT_RENDER_MODE_LCD );

            int _h = m_face->glyph->bitmap.rows;
            int _w = m_face->glyph->bitmap.width/3;
            int _p = m_face->glyph->bitmap.pitch;

            uchar *src = m_face->glyph->bitmap.buffer;
            glyphImage = new QImage(_w, _h, QImage::Format_ARGB32);

            int bit = 0; // address in buffer
            for (int y = 0; y < _h; y++) {

                for (int x = 0; x < _w; x++) {

                    uchar r = 0xff - src[bit++];
                    uchar g = 0xff - src[bit++];
                    uchar b = 0xff - src[bit++];

                    // filtering out any whites:
                    if (r + g + b >= 3 * 0xff) {
                        continue;
                    }

                    glyphImage->setPixel(x, y, qRgb(r, g, b)); //
pixel coordinates to color value

                }

                bit = _p * (y + 1); // go to next line, start from 0
            }

On Wed, Jun 15, 2011 at 7:20 PM, Collyer, Oliver, SI
<oliver.collyer@sigames.com> wrote:
> The light hinting more or less just hints in the vertical direction, so this is \
> compatible with LCD rendering which deals with the horizontal (assuming your LCD \
> display is a regular one and your text is horizontal). IMO it's a pretty good \
> combination. 
> To display an LCD-rendered source bitmap on the screen you basically use each \
> triplet of values in the source as the respective intensity/alpha values of the RGB \
> components of your destination pixel. 
> i.e:
> 
> - the first (left) value in the source triplet gives how much of the R of your text \
> colour to use when blending (so a value of 255 means use all of the text colour R \
> and don't mix it with any of the background bitmap R, whereas a value of 128 would \
>                 mean mix them 50-50, etc)
> - the second (middle) value in the source triplet gives how much of the G of your \
>                 text colour to use when blending
> - the third (right) value in the source triplet gives how much of the B of your \
> text colour to use when blending 
> This assumes you have already filtered your LCD bitmap first. FreeType has \
> functionality for doing this, and this basically reduces a problem known as 'colour \
> fringing' by mixing together neighbouring pixels in the bitmap. 
> Here is a decent resource that describes the basics:
> 
> http://www.grc.com/ctwhat.htm
> 
> Hope this helps.
> 
> On 15 Jun 2011, at 18:58, Aekold Helbrass wrote:
> 
> > Good day All!
> > 
> > I've read the note to
> > http://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#FT_LOAD_TARGET_XXX
> >  and now I have a question: what will I get in case of using LIGHT for
> > loading and LCD for rendering? Is it considered bad practice, or it
> > may be used to achieve some special results?
> > 
> > And the second question - the reason why I can't check the first one
> > for myself. I am using that awesome Qt example (example4.cpp) to see
> > how freetype works in general, but I can't get proper LCD modes. I see
> > that image is 3 times wider and divide it, but it's still crippled
> > when rendered. I suppose I should use some other color table or some
> > smart pixel filtering methods that are used in openjdk or qt, but I am
> > not familiar with freetype enough to figure it out myself. So, if
> > there are some LCD rendering examples or guides - please give me some
> > links.
> > 
> > Thanx!
> > 
> > _______________________________________________
> > Freetype mailing list
> > Freetype@nongnu.org
> > https://lists.nongnu.org/mailman/listinfo/freetype
> 
> 


["snapshot04.png" (image/png)]

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